1. Field of the Invention
The present invention relates to a method and apparatus for maintaining tape tension in a tape cartridge, particularly in a tape cartridge of the type used in high-speed data storage and retrieval systems.
2. Description of the Prior Art
In a conventional belt-driven data cartridge, as is referred to in the art as a Quarter Inch Cartridge or QIC, for use in a data storage and retrieval system, wherein the data is stored on and retrieved from a reeled magnetic tape, the tape in the transport is caused to move over a read/write head by means of which new data is written on, or existing data is read from, the moving tape. In such known cartridges, the tape is moved by a rubber belt which is entrained around the respective exterior tape layer on each of the feed reel and the take-up reel. The belt is also entrained around a drive roller within the cartridge, which engages an external drive roller located in a drive unit and, rotated by a drive motor, when the cartridge is inserted in the drive unit.
In such known belt-driven cartridges, there is no mechanical access to the tape or to the feed and take-up reels, since they are incased in the cartridge housing. Therefore, in order to maintain the tension in the tape at a proper level so that the tape is taut against the write/read head, the belt is entrained around two tension rollers in the cartridge. The tape must be moving for tension to be created.
In such systems a large number of so-called start/stop events occur. With each start/stop event the tape is braked and must be rewound a short distance to bring the tape to a location adjacent the write/read head at which data entry or data reaching ceased. Since each small rewind creates a slight loss of tension (but the tension does not drop to zero), as such start/stop events accumulate, the tape becomes increasingly slack.
Another problem caused by slackness in the tape is that, if the tape is to be rewound so as to bring a particular tape location to be disposed adjacent the write/read head, the slackness in the tape will reduce the accuracy with which the tape can be positioned, so that the desired tape location may not be precisely disposed in front of the write/read head.
A detailed discussion of the phenomenon of tape tension in cartridges of this type is found in 3M Field Bulletin Data Cartridges, No. 28, Nov. 7, 1990.